Sounding reference signals and channel state information reference signals enhancements for coordinated multipoint communications

ABSTRACT

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a user equipment (UE). The apparatus may transmit a supported configuration of the UE for at least one of SRS transmission or CSI-RS reception for communication with a plurality of TRPs. The apparatus may receive, in response to transmitting the supported configuration, configuration information for at least one of the SRS transmission or the CSI-RS reception, wherein the configuration information is generated based on the supported configuration. The apparatus may communicate, with at least a subset of the plurality of TRPs, using at least one of the SRS transmission or the CSI-RS reception on resource elements assigned based on the configuration information. A base station connected to the TRPs may use the SRS/CSI-RS for cluster management and scheduling or to estimate downlink channels to determine precoding for downlink transmissions.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of Greek Application No.20180100309, entitled “Sounding Reference Signals and Channel StateInformation Reference Signals Enhancements for Coordinated MultipointCommunications” and filed on Jul. 9, 2018, which is expresslyincorporated by reference herein in its entirety.

BACKGROUND Technical Field

The present disclosure relates generally to communication systems, andmore particularly, to coordinated multipoint (CoMP) communications.

Introduction

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis 5G New Radio (NR). 5G NR is part of a continuous mobile broadbandevolution promulgated by Third Generation Partnership Project (3GPP) tomeet new requirements associated with latency, reliability, security,scalability (e.g., with Internet of Things (IoT)), and otherrequirements. Some aspects of 5G NR may be based on the 4G Long TermEvolution (LTE) standard. There exists a need for further improvementsin 5G NR technology. These improvements may also be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

In an aspect of the disclosure, a method, a computer-readable medium,and an apparatus are provided. In certain configurations, the apparatusmay be a user equipment (UE). The apparatus may transmit a supportedconfiguration of the UE for at least one of sounding reference signal(SRS) transmission or channel state information reference signal(CSI-RS) reception for communication with a plurality of transmissionreception points (TRPs). The apparatus may receive, in response totransmitting the supported configuration, configuration information forat least one of the SRS transmission or the CSI-RS reception, whereinthe configuration information is generated based on the supportedconfiguration. The apparatus may communicate, with at least a subset ofthe plurality of TRPs, using at least one of the SRS transmission or theCSI-RS reception on resource elements assigned based on theconfiguration information.

In certain other configurations, the apparatus may be a base station.The base station may be associated with one or more TRPs. The apparatusmay receive a supported configuration by the UE of at least one of a SRStransmission and a CSI-RS reception for communication with a pluralityof TRPs. The base station may generate configuration information for atleast one of the SRS transmission and the CSI-RS reception by the UE.The configuration information may be generated based on the UE'ssupported configuration. The base station may transmit the generatedconfiguration information to the UE. The base station may communicatewith the UE through one or more TRPs using at least one of the SRStransmission and the CSI-RS reception on resource elements assignedbased on the configuration information.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating examples of a first5G/NR frame, DL channels within a 5G/NR subframe, a second 5G/NR frame,and UL channels within a 5G/NR subframe, respectively.

FIG. 3 is a diagram illustrating an example of a base station and userequipment (UE) in an access network.

FIG. 4 is a diagram illustrating an example factory that may deploy CoMPin accordance with certain aspects of the disclosure.

FIG. 5 illustrates a wireless communication system that may use jointtransmission (JT)-CoMP in accordance with certain aspects of thedisclosure.

FIG. 6 is a call flow diagram illustrating an implementation ofcommunication between a UE and a TRP of supported configurationinformation of the UE, programmed configuration information from theTRP, and the transmission and reception of SRS and CSI-RS based on theprogrammed configuration information in accordance with certain aspectsof the disclosure.

FIG. 7 illustrates a configuration of using every resource element orsubcarrier over a span of two resource blocks in a slot to transmit SRSresources from a UE to support precoding for downlink transmissions inaccordance with certain aspects of the disclosure.

FIG. 8 illustrates a configuration of using one of every 36 resourceelements or subcarriers over a number of resource blocks in a slot totransmit SRS resources from a UE to support cluster management andscheduling in accordance with certain aspects of the disclosure.

FIG. 9 is a flowchart of a method of wireless communication that may beimplemented by a UE in accordance with certain aspects of thedisclosure.

FIG. 10 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus ofa UE in accordance with certain aspects of the disclosure.

FIG. 11 is a diagram illustrating an example of a hardwareimplementation for an apparatus of a UE employing a processing system inaccordance with certain aspects of the disclosure.

FIG. 12 is a flowchart of a method of wireless communication that may beimplemented by a base station in accordance with certain aspects of thedisclosure.

FIG. 13 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus ofa base station in accordance with certain aspects of the disclosure.

FIG. 14 is a diagram illustrating an example of a hardwareimplementation for an apparatus of a base station employing a processingsystem in accordance with certain aspects of the disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, an Evolved Packet Core (EPC) 160, and anothercore network 190 (e.g., a 5G Core (5GC)). The base stations 102 mayinclude macrocells (high power cellular base station) and/or small cells(low power cellular base station). The macrocells include base stations.The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to asEvolved Universal Mobile Telecommunications System (UMTS) TerrestrialRadio Access Network (E-UTRAN)) may interface with the EPC 160 throughbackhaul links 132 (e.g., S1 interface). The base stations 102configured for 5G NR (collectively referred to as Next Generation RAN(NG-RAN)) may interface with core network 190 through backhaul links184. In addition to other functions, the base stations 102 may performone or more of the following functions: transfer of user data, radiochannel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter-cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160 or corenetwork 190) with each other over backhaul links 134 (e.g., X2interface). The backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacrocells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz)bandwidth per carrier allocated in a carrier aggregation of up to atotal of Yx MHz (x component carriers) used for transmission in eachdirection. The carriers may or may not be adjacent to each other.Allocation of carriers may be asymmetric with respect to DL and UL(e.g., more or fewer carriers may be allocated for DL than for UL). Thecomponent carriers may include a primary component carrier and one ormore secondary component carriers. A primary component carrier may bereferred to as a primary cell (PCell) and a secondary component carriermay be referred to as a secondary cell (SCell).

Certain UEs 104 may communicate with each other using device-to-device(D2D) communication link 158. The D2D communication link 158 may use theDL/UL WWAN spectrum. The D2D communication link 158 may use one or moresidelink channels, such as a physical sidelink broadcast channel(PSBCH), a physical sidelink discovery channel (PSDCH), a physicalsidelink shared channel (PSSCH), and a physical sidelink control channel(PSCCH). D2D communication may be through a variety of wireless D2Dcommunications systems, such as for example, FlashLinQ, WiMedia,Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

A base station 102, whether a small cell 102′ or a large cell (e.g.,macro base station), may include an eNB, gNodeB (gNB), or another typeof base station. Some base stations, such as gNB 180 may operate in atraditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies,and/or near mmW frequencies in communication with the UE 104. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band (e.g., 3 GHz-300 GHz) hasextremely high path loss and a short range. The mmW base station 180 mayutilize beamforming 182 with the UE 104 to compensate for the extremelyhigh path loss and short range.

The base station 180 may transmit a beamformed signal to the UE 104 inone or more transmit directions 182′. The UE 104 may receive thebeamformed signal from the base station 180 in one or more receivedirections 182″. The UE 104 may also transmit a beamformed signal to thebase station 180 in one or more transmit directions. The base station180 may receive the beamformed signal from the UE 104 in one or morereceive directions. The base station 180/UE 104 may perform beamtraining to determine the best receive and transmit directions for eachof the base station 180/UE 104. The transmit and receive directions forthe base station 180 may or may not be the same. The transmit andreceive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMES 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService, and/or other IP services. The BM-SC 170 may provide functionsfor MBMS user service provisioning and delivery. The BM-SC 170 may serveas an entry point for content provider MBMS transmission, may be used toauthorize and initiate MBMS Bearer Services within a public land mobilenetwork (PLMN), and may be used to schedule MBMS transmissions. The MBMSGateway 168 may be used to distribute MBMS traffic to the base stations102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN)area broadcasting a particular service, and may be responsible forsession management (start/stop) and for collecting eMBMS relatedcharging information.

The core network 190 may include a Access and Mobility ManagementFunction (AMF) 192, other AMFs 193, a Session Management Function (SMF)194, and a User Plane Function (UPF) 195. The AMF 192 may be incommunication with a Unified Data Management (UDM) 196. The AMF 192 isthe control node that processes the signaling between the UEs 104 andthe core network 190. Generally, the AMF 192 provides QoS flow andsession management. All user Internet protocol (IP) packets aretransferred through the UPF 195. The UPF 195 provides UE IP addressallocation as well as other functions. The UPF 195 is connected to theIP Services 197. The IP Services 197 may include the Internet, anintranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service,and/or other IP services.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), a transmit reception point(TRP), or some other suitable terminology. The base station 102 providesan access point to the EPC 160 or core network 190 for a UE 104.Examples of UEs 104 include a cellular phone, a smart phone, a sessioninitiation protocol (SIP) phone, a laptop, a personal digital assistant(PDA), a satellite radio, a global positioning system, a multimediadevice, a video device, a digital audio player (e.g., MP3 player), acamera, a game console, a tablet, a smart device, a wearable device, avehicle, an electric meter, a gas pump, a large or small kitchenappliance, a healthcare device, an implant, a sensor/actuator, adisplay, or any other similar functioning device. Some of the UEs 104may be referred to as IoT devices (e.g., parking meter, gas pump,toaster, vehicles, heart monitor, etc.). The UE 104 may also be referredto as a station, a mobile station, a subscriber station, a mobile unit,a subscriber unit, a wireless unit, a remote unit, a mobile device, awireless device, a wireless communications device, a remote device, amobile subscriber station, an access terminal, a mobile terminal, awireless terminal, a remote terminal, a handset, a user agent, a mobileclient, a client, or some other suitable terminology.

In CoMP, the base station 102/180 may use reference signals, such assounding reference signal (SRS) resources transmitted from a UE 104 tothe base station 102/180 and channel state information reference signal(CSI-RS) resources transmitted from the base station 102/180 to the UE104, to obtain link quality estimates. The base station may use the linkquality estimates of uplink channels and downlink channels between thebase station 102/180 and the UE 104 for cluster management andscheduling, such as identifying the TRPs or other base stationsassociated with the base station 102/180 that will be cooperating totransmit to the UE 104. FIG. 1 illustrates an example of multiple TRPs107 associated with base station 102/180. As an example, FIG. 1illustrates a UE 104 receiving CoMP communication 109 from multiple TRPs107 associated with base station 102/180. The UE may be associated withfactory equipment involved in factory automation, as an example.

The base station 102/180 may also use the SRS resources received fromthe UE 104 to estimate downlink channels to determine precoding for thedownlink channels between the base station 102/180 and the UE 104 whenthe downlink channels and the uplink channels are similar, such as in aTDD system. The base station 102/180 may adapt downlink transmissionsfrom the base station 102/180 to the UE 104 by precoding the downlinktransmission based on the SRS resources.

In certain aspects, the UE 104 may comprise a CoMP SRS/CSI-RS component199 configured to transmit to the base station 180 supportedconfiguration of at least one of a SRS transmission and a CSI-RSreception and to receive configuration information from the base station180 for at least one of the SRS transmission and the CSI-RS reception.The UE 104 may transmit SRS resources to the base station 180 andreceive CSI-RS resources from the base station 180 based on resourceelements assigned according to the configuration information, e.g., asdescribed below in connection with any of FIGS. 2A-12. Similarly, thebase station 180 may comprise a CoMP SRS/CSI-RS component 198 configuredto receive configuration information from the UE 104 for at least one ofthe SRS transmission and the CSI-RS reception, and to transmitconfiguration information to the UE 104 for at least one of the SRStransmission and the CSI-RS reception by the UE 104. The base station180 may receive SRS resources from the UE 104 and transmit CSI-RSresources to the UE 104 based on resource elements assigned according tothe configuration information, e.g., as described below in connectionwith any of FIGS. 2A-12. Although the following description may befocused on 5G NR, the concepts described herein may be applicable toother similar areas, such as LTE, LTE-A, CDMA, GSM, and other wirelesstechnologies.

FIG. 2A is a diagram 200 illustrating an example of a first subframewithin a 5G/NR frame structure. FIG. 2B is a diagram 230 illustrating anexample of DL channels within a 5G/NR subframe. FIG. 2C is a diagram 250illustrating an example of a second subframe within a 5G/NR framestructure. FIG. 2D is a diagram 280 illustrating an example of ULchannels within a 5G/NR subframe. The 5G/NR frame structure may be FDDin which for a particular set of subcarriers (carrier system bandwidth),subframes within the set of subcarriers are dedicated for either DL orUL, or may be TDD in which for a particular set of subcarriers (carriersystem bandwidth), subframes within the set of subcarriers are dedicatedfor both DL and UL. In the examples provided by FIGS. 2A, 2C, the 5G/NRframe structure is assumed to be TDD, with subframe 4 being configuredwith slot format 28 (with mostly DL), where D is DL, U is UL, and X isflexible for use between DL/UL, and subframe 3 being configured withslot format 34 (with mostly UL). While subframes 3, 4 are shown withslot formats 34, 28, respectively, any particular subframe may beconfigured with any of the various available slot formats 0-61. Slotformats 0, 1 are all DL, UL, respectively. Other slot formats 2-61include a mix of DL, UL, and flexible symbols. UEs are configured withthe slot format (dynamically through DL control information (DCI), orsemi-statically/statically through radio resource control (RRC)signaling) through a received slot format indicator (SFI). Note that thedescription infra applies also to a 5G/NR frame structure that is TDD.

Other wireless communication technologies may have a different framestructure and/or different channels. A frame (10 ms) may be divided into10 equally sized subframes (1 ms). Each subframe may include one or moretime slots. Subframes may also include mini-slots, which may include 7,4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on theslot configuration. For slot configuration 0, each slot may include 14symbols, and for slot configuration 1, each slot may include 7 symbols.The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. Thesymbols on UL may be CP-OFDM symbols (for high throughput scenarios) ordiscrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (alsoreferred to as single carrier frequency-division multiple access(SC-FDMA) symbols) (for power limited scenarios; limited to a singlestream transmission). The number of slots within a subframe is based onthe slot configuration and the numerology. For slot configuration 0,different numerologies μ 0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots,respectively, per subframe. For slot configuration 1, differentnumerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, persubframe. Accordingly, for slot configuration 0 and numerology μ, thereare 14 symbols/slot and 2 ^(μ) slots/subframe. The subcarrier spacingand symbol length/duration are a function of the numerology. Thesubcarrier spacing may be equal to 2^(μ)*15 kHz, where μ is thenumerology 0 to 5. As such, the numerology μ=0 has a subcarrier spacingof 15 kHz and the numerology μ=5 has a subcarrier spacing of 480 kHz.The symbol length/duration is inversely related to the subcarrierspacing. FIGS. 2A-2D provide an example of slot configuration 0 with 14symbols per slot and numerology μ=0 with 1 slot per subframe. Thesubcarrier spacing is 15 kHz and symbol duration is approximately 66.7μs.

A resource grid may be used to represent the frame structure. Each timeslot includes a resource block (RB) (also referred to as physical RBs(PRBs)) that extends 12 consecutive subcarriers. The resource grid isdivided into multiple resource elements (REs). The number of bitscarried by each RE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry reference (pilot)signals (RS) for the UE. The RS may include demodulation RS (DM-RS)(indicated as R_(x) for one particular configuration, where 100x is theport number, but other DM-RS configurations are possible) and channelstate information reference signals (CSI-RS) for channel estimation atthe UE. The RS may also include beam measurement RS (BRS), beamrefinement RS (BRRS), and phase tracking RS (PT-RS).

FIG. 2B illustrates an example of various DL channels within a subframeof a frame. The physical downlink control channel (PDCCH) carries DCIwithin one or more control channel elements (CCEs), each CCE includingnine RE groups (REGs), each REG including four consecutive REs in anOFDM symbol. A primary synchronization signal (PSS) may be within symbol2 of particular subframes of a frame. The PSS is used by a UE 104 todetermine subframe/symbol timing and a physical layer identity. Asecondary synchronization signal (SSS) may be within symbol 4 ofparticular subframes of a frame. The SSS is used by a UE to determine aphysical layer cell identity group number and radio frame timing. Basedon the physical layer identity and the physical layer cell identitygroup number, the UE can determine a physical cell identifier (PCI).Based on the PCI, the UE can determine the locations of theaforementioned DM-RS. The physical broadcast channel (PBCH), whichcarries a master information block (MIB), may be logically grouped withthe PSS and SSS to form a synchronization signal (SS)/PBCH block. TheMIB provides a number of RBs in the system bandwidth and a system framenumber (SFN). The physical downlink shared channel (PDSCH) carries userdata, broadcast system information not transmitted through the PBCH suchas system information blocks (SIBs), and paging messages.

As illustrated in FIG. 2C, some of the REs carry DM-RS (indicated as Rfor one particular configuration, but other DM-RS configurations arepossible) for channel estimation at the base station. The UE maytransmit DM-RS for the physical uplink control channel (PUCCH) and DM-RSfor the physical uplink shared channel (PUSCH). The PUSCH DM-RS may betransmitted in the first one or two symbols of the PUSCH. The PUCCHDM-RS may be transmitted in different configurations depending onwhether short or long PUCCHs are transmitted and depending on theparticular PUCCH format used. Although not shown, the UE may transmitsounding reference signals (SRS). The SRS may be used by a base stationfor channel quality estimation to enable frequency-dependent schedulingon the UL.

FIG. 2D illustrates an example of various UL channels within a subframeof a frame. The PUCCH may be located as indicated in one configuration.The PUCCH carries uplink control information (UCI), such as schedulingrequests, a channel quality indicator (CQI), a precoding matrixindicator (PMI), a rank indicator (RI), and HARQ ACK/NACK feedback. ThePUSCH carries data, and may additionally be used to carry a bufferstatus report (BSR), a power headroom report (PHR), and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with aUE 350 in an access network. In the DL, IP packets from the 5GC 160 maybe provided to a controller/processor 375. The controller/processor 375implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a packet dataconvergence protocol (PDCP) layer, a radio link control (RLC) layer, anda medium access control (MAC) layer. The controller/processor 375provides RRC layer functionality associated with broadcasting of systeminformation (e.g., MIB, SIBs), RRC connection control (e.g., RRCconnection paging, RRC connection establishment, RRC connectionmodification, and RRC connection release), inter radio access technology(RAT) mobility, and measurement configuration for UE measurementreporting; PDCP layer functionality associated with headercompression/decompression, security (ciphering, deciphering, integrityprotection, integrity verification), and handover support functions; RLClayer functionality associated with the transfer of upper layer packetdata units (PDUs), error correction through ARQ, concatenation,segmentation, and reassembly of RLC service data units (SDUs),re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto transport blocks(TBs), demultiplexing of MAC SDUs from TBs, scheduling informationreporting, error correction through HARQ, priority handling, and logicalchannel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 350. If multiple spatial streams are destined for the UE 350,they may be combined by the RX processor 356 into a single OFDM symbolstream. The RX processor 356 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe base station 310. These soft decisions may be based on channelestimates computed by the channel estimator 358. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the base station 310 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 359, which implements layer 3 and layer 2functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. In the UL, the controller/processor 359provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the 5GC 160. Thecontroller/processor 359 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the base station 310, the controller/processor 359provides RRC layer functionality associated with system information(e.g., MIB, SIBs) acquisition, RRC connections, and measurementreporting; PDCP layer functionality associated with headercompression/decompression, and security (ciphering, deciphering,integrity protection, integrity verification); RLC layer functionalityassociated with the transfer of upper layer PDUs, error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC SDUs,re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto TBs,demultiplexing of MAC SDUs from TBs, scheduling information reporting,error correction through HARQ, priority handling, and logical channelprioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by the base station 310 may be used bythe TX processor 368 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 368 may be provided to different antenna352 via separate transmitters 354TX. Each transmitter 354TX may modulatean RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a mannersimilar to that described in connection with the receiver function atthe UE 350. Each receiver 318RX receives a signal through its respectiveantenna 320. Each receiver 318RX recovers information modulated onto anRF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. In the UL, the controller/processor 375provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 350. IP packets from thecontroller/processor 375 may be provided to the 5GC 160. Thecontroller/processor 375 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

At least one of the TX processor 368, the RX processor 356, and thecontroller/processor 359 may be configured to perform aspects inconnection with 199 of FIG. 1.

At least one of the TX processor 316, the RX processor 370, and thecontroller/processor 375 may be configured to perform aspects inconnection with 198 of FIG. 1.

A base station may use CoMP techniques to communicate between multiple

TRPs associated with a base station and one or more UE. CoMP techniquesmay include a coherent joint transmission technique, a non-coherentjoint transmission technique, and/or a muting technique to improvespatial diversity with a UE. As an example, CoMP may be employed in FA.The base station may use spatial diversity techniques among the TRPswhen communicating with a UE to realize ultra-reliability and lowlatency communication (URLLC) (e.g., less than 1 ms latency and 10⁻⁶reliability). FIG. 4 is a diagram illustrating an example factoryenvironment 400 that may deploy CoMP in accordance with certain aspectsof the disclosure. The factory environment 400 may include, e.g., atleast one sensor/actuator (S/A) 402, at least one programmable logiccontroller (PLC) 404, at least one human machine interface (HMI) 406,and at least one management system 408. The SA 402, the PLC 404, the HMI406, and/or the management system 408 may correspond to UEs, e.g., UE104, 350, that receive wireless communication from a base station, e.g.,102, 180, 310.

In certain implementations, an S/A 402 may include one or more devicecomponents, e.g., such as a rotary motor, linear servo, and/or positionsensor, just to name a few. An S/A 402 may receive one or more commands(e.g., instructing motion) from at least one PLC 404, and the S/A 402may send sensor information (e.g., related to the motion, position,acceleration of the device or a component of the device). Multiple PLCs404 may coordinate with one another in order to assure the correctinstructions are sent to an S/A 402, and/or to act as a relay between anHMI 406 and an S/A 402.

An HMI 406 may include, e.g., a tablet device, a handheld device, awireless device, a panel device, a wearable device, a virtual reality(VR) device, and/or an augmented reality (AR) device, just to name afew. An HMI 406 may control an S/A 402. For example, a user may inputinstructions into the HMI 406 such as “start” or “stop,” in order tocontrol the motion and/or actions of an SA 402. In another example, auser may input instructions into the HMI such as “change mode from‘widget 1’ to ‘widget 2.’” Instructions input into an HMI 406 may besent to a PLC 404, and the PLC 404 may configure the instructions (e.g.,using custom hardware) so that the instructions may be understood by anS/A 402.

The management system 408 may include, e.g., one or more of anindustrial personal computer (PC), controller programming, software,security management, and/or provide long term key performance indicator(KPI) (e.g., a value that demonstrates how effectively the examplefactory environment 400 is achieving key business objectives). Themanagement system 408 may receive information related to KPI from one ormore HMIs 406. The management system 408 may send instructions to one ormore of the HMI(s) 406, PLC(s) 404, and/or S/A(s) 402.

The example factory environment 400 may include, e.g., multipleproduction cells (e.g., 2, 10, 100, 1000, 10000, etc.), and eachproduction cell may have dimensions of, e.g., 10 m×10 m×3 m. Eachproduction cell may include multiple S/As 402. An example productioncell may include, e.g., 1-50 S/As 402 or more than 50 S/As 402.

Communications between devices in the example factory environment 400may be effected, e.g., using one or more base stations, nodes, and/orTRPs (e.g., TRPs 107) located within a production cell. Forcommunications relating to factory automation, one objective may be tomeet latency and/or reliability target threshold(s) in the presence ofsignal fading, shadowing, and/or other scenarios that may occur in afactory environment in which moving parts and/or reflective surfaces mayobstruct the line of sight between a sending device (e.g., TRP, UE, PLC,S/A, etc.) and a receiving device (e.g., TRP, UE, PLC, S/A, etc.).

To meet certain latency and/or reliability target thresholds such as anultra-reliability and low latency configuration (URLLC) (e.g., less than1 ms latency and 10⁻⁶ reliability) within a factory setting, a wirelesscommunication system may exploit spatial diversity. Spatial diversitymay be achieved using multiple TRPs (e.g., TRPs 107) and/or basestations that communicate with the UE. The TRPs may employ concurrentjoint transmission (JT)-CoMP communications to a UE, non-coherent jointtransmission communications to a UE, or a muting technique where one ormore TRPs are muted and others are transmitting in resources assignedfor communications with a UE.

FIG. 5 illustrates a wireless communication network 500 that may useCoMP in accordance with certain aspects of the disclosure. The wirelesscommunication network 500 may be used in, e.g., the example factoryenvironment 400 described above in connection with FIG. 4. The wirelesscommunication network 500 may include a first TRP 502 a located in afirst cell 501 a, a second TRP 502 b located in a second cell 501 b, aUE 504 located at a cell edge of the first cell 501 a and the secondcell 501 b, and a moveable device 506 that may be used in an automatedprocess. The first TRP 502 a and second TRP 502 b may each correspondto, e.g., a base station, e.g., base station 102, 180, 310. The firstTRP 502 a and the second TRP 502 b may be connected to a central unit(CU) that may connect to other TRPs. In one aspect, the CU may be partof a base station, e.g., base station 102, 180, 310. In one aspect, thebase station may include one or more of a CU, one or more distributedunits, and multiple TRPs. The UE 504 may correspond to, e.g., UE 104,350. The UE 504 may also correspond to any of the S/A 402, the PLC 404,the HMI 406, or the management system 408 in FIG. 4. Although two TRPs502 a, 502 b are illustrated in FIG. 5, the wireless communicationsystem 500 may include more than two TRPs 502 a, 502 b that may be usedas a CoMP cluster for sending CoMP communications to the UE 504.

To meet requirements for URLLC within a factory environment, thewireless communication network 500 may perform CoMP by sendingconcurrent downlink transmissions 503 a, 503 b from multiple TRPs 502 a,502 b (e.g., a CoMP cluster) to the UE 504. However, the performancegains achieved using CoMP may be sensitive to channel estimation errorsthat may arise when a moveable device 506 obstructs the direction inwhich a downlink transmission 503 a is sent, and/or when the UE 504moves throughout the network.

A CU or a base station connected to the CoMP cluster of TRPs mayidentify which TRPs may cooperate to transmit to the UE 504 as part ofcluster management and scheduling. The base station may use referencesignals, such as SRS transmitted by UE 504 and received by TRPs 502 a,502 b, and CSI-RS transmitted by TRPs 502 a, 502 b to UE 504, to obtainlink quality estimates of uplink channels and downlink channels betweenTRPs 502 a, 502 b and UE 504. For example, the base station mayconfigure the UE to transmit the SRS on resource elements in a slot. TheUE may transmit the SRS on the configured resource elements and the basestation may measure the received SRS. The base station may use the SRSmeasurements to generate an uplink channel estimate and downlink channelestimates for cluster management and scheduling. The base station mayalso use the downlink channel estimates to determine precoding to adaptdownlink transmissions from the TRPs 502 a and 502 b to the UE 504.Aspects presented herein improve the allocations and use of SRSresources and CSI-RS for cluster management and scheduling and/or forprecoding in CoMP. Aspects help to improve the efficient use of wirelessresources and reduction in power consumption while meeting the uniqueneeds of CoMP, e.g., including cluster management, scheduling and/orprecoding.

FIG. 6 is a call flow diagram 600 illustrating example aspects ofcommunication between a UE 602 and a TRP 604. The communication mayinclude supported configuration information of the UE, programmedconfiguration information from the TRP, and the transmission andreception of SRS and CSI-RS based on the programmed configurationinformation in accordance with certain aspects of the disclosure. TheTRP 604 may be part of a CoMP cluster that may connect to a basestation, e.g., base station 102, 180, 310.

In 606, the UE 602 may transmit its supported configuration for uplinkSRS transmission to the TRP 604 and/or its supported configuration fordownlink CSI-RS reception from the TRP 604. As mentioned, the TRP 604 orthe base station connected to the TRP 604 may measure the SRS resourcestransmitted from the UE 602 to estimate the downlink channel between theTRP 604 and the UE 602 to determine precoding to be applied to downlinktransmission when the downlink channels and the uplink channels aresimilar, such as in a time domain duplex (TDD) system. The UE 602 maytransmit the SRS on resource elements in one or more resource blocks ina slot (e.g., in the last symbol of a subframe).

SRS may be transmitted up to a maximum density of one of every 2resource elements (e.g., comb-2 SRS transmission) over a span of atleast 4 resource blocks in a symbol (a resource element in a symbol mayalso be referred to as a subcarrier). However, a different density maybe needed to use the SRS to estimate a downlink channel for precodingpurposes. Aspects presented herein enable use of a higher density of theresource elements in a slot to transmit the SRS, which may lead to moreaccurate estimates of the downlink channel and thus more accurateprecoding of the downlink transmissions from the TRP 604 to the UE 602,the UE 602 may support transmitting the SRS on every resource element(e.g., comb-1 SRS transmission).

For example, to meet URLLC requirements in factory automation, the CoMPmay send small downlink packets that only occupy one resource block.Thus, having a UE transmit the SRS over a span of a minimum of fourresource blocks may lead to a waste of wireless resource and powerconsumption at the UE. To reduce resource consumption and processingoverhead, the UE 602 may support transmitting the SRS on the resourceelements in less than 4 resource blocks. In one aspect, the UE 602 maysupport transmitting the SRS over a span of an integer number ofresource blocks in a slot with a granularity of one resource block. Inone aspect, the UE 602 may support transmitting the SRS on everyresource element over a span of less than 4 resource blocks (e.g., 1, 2,or 3 resource blocks) in a slot. Thus, the UE may transmit SRS thatoccupies every resource element in a single resource block. Transmissionof the SRS on every resource element (e.g., each subcarrier in a symbol)in one or more resource blocks in a slot may be referred to as a comb-1SRS transmission.

The TRP 604 or the base station connected to the TRP 604 may measure theSRS received from the UE 602 to estimate the downlink channel forcluster management and scheduling. For example, the base stationconnected to a group of TRPs may measure the SRS received at a number ofthe TRPs to obtain link quality estimates from the group of TRPs to theUE 602. The base station may use the link quality estimates to identifya subset of the TRPs that may cooperate to transmit to the UE 602. Theresource elements required to estimate the downlink channel for clustermanagement and scheduling may not be as high as the resource elementsrequired to estimate the downlink channel for the precodingdetermination. Nevertheless, the resource consumption required scaleswith the density of the resource elements used for the SRS and thenumber of UEs in the CoMP. A UE may be able to transmit the SRS down toa minimum density of one of every 4 resource elements (e.g., comb-4 SRStransmission). However, this density may be beyond what is needed forcluster management and scheduling. Thus, the transmission of SRS with adensity of one of every four resource elements may cause an inefficientuse of power and wireless resources. In one aspect, to reduce thedensity of SRS transmission further, the UE 602 may support transmittingthe SRS on one of every N resource elements (subcarriers) over a span ofa number of resource blocks in a slot, where N is greater than 4.

In one aspect, the UE 602 may measure a received CSI-RS transmitted fromthe TRP 604 to estimate the downlink channel. The UE 602 may transmitthe link quality estimates of the downlink channel to the TRP 604 forthe TRP 604 or the base station connected to the TRP 604 to performcluster management and scheduling. Similar to the resource requirementfor the SRS, the resource requirement for the CSI-RS scales with thedensity of the resource elements used for the CSI-RS transmissions andthe number of UEs in the CoMP. CSI-RS with a minimum density of one ofevery 24 resource elements over a minimum of 24 resource blocks, maylead to an inefficient use of wireless resources and power. Such adensity may be more than needed for cluster management/scheduling forCoMP. In one aspect, to reduce the density of CSI-RS transmission by theTRP 604, the UE 602 may support receiving the CSI-RS on one of every Nresource elements over a span of a number of resource blocks in a slot,where N is greater than 24. In one aspect, the UE 602 may supportreceiving the CSI-RS over a span of less than 2 resource blocks in aslot. In one aspect, the UE 602 may support receiving more than athreshold number of CSI-RS resources from a number of TRPs connectedwith the base station during a slot. In one aspect, the threshold numberof CSI-RS resources received in a slot includes a threshold number ofnon-zero power (NZP) CSI-RS resources received in a component carrierduring a slot, where the threshold number of NZP CSI-RS resources isgreater than 32.

The TRP 604 may receive the information indicating the configurationsupported by the UE 602 for uplink SRS transmission and for downlinkCSI-RS reception. The TRP 604 or the base station connected to the TRP604 may generate, at 610, configuration information for SRStransmission(s) from the UE 602 to the TRP 604 or configurationinformation for reception by the UE 602 of CSI-RS(s) transmitted fromthe TRP 604 based on the supported configuration of the UE 602. Thesupported configuration of the UE 602 may set the upper bounds of theconfiguration information generated for the UE 602. For example, if theUE 602 supports comb-1 SRS transmissions over a span of less than 4resource blocks in a slot, the TRP 604 or the base station connected tothe TRP 604 may generate configuration information for the UE 602 totransmit the SRS on every resource element over a span of 1 resourceblock in a slot for the TRP 604 or the base station connected to the TRP604, e.g., to enable the TRP to estimate the downlink channel fordownlink transmission precoding. In another example, if the UE 602supports greater than comb-4 SRS transmissions over a number of resourceblocks in a slot, the TRP 604 or the base station connected to the TRP604 may generate configuration information for the UE 602 to transmitthe SRS on one of every 5 resource elements over a span of two resourceblocks in a slot for the TRP 604 or the base station connected to theTRP 604, e.g., to enable the TRP to estimate the downlink channel forcluster management and scheduling.

In one aspect, the configuration information generated at 610 mayinclude a periodicity of the resource blocks, slots, subframes, etc.,used for the SRS transmissions. The configuration information mayinclude a sequence and a cyclic shift of the sequence used to transmitthe SRS. The configuration information may include a time hoppingsequence used to transmit the SRS. The configuration information mayinclude a comb-offset range. The configuration information may include aposition of the first resource element and/or a position of the lastresource element in addition to the comb value. The resource elementsused for the SRS transmission may be configured to use a sequence and acyclic shift of the sequence in the time domain or a phase ramp in thefrequency domain. In this way, different UEs may use the same resourceelements for the transmissions of their respective SRS resources byusing different cyclic shifts of a sequence or using differentsequences. In one aspect, the set of cyclic shifts for a sequence thatmay be used for the SRS transmissions may depend on the comb value ofthe SRS resources (e.g., comb-2 or comb-4). In one aspect, the number ofcyclic shifts for a sequence may also depend on the number of resourceelements or subcarriers in a symbol used for the SRS transmissions. Forexample, if 30 resource elements in a symbol are used for the SRStransmissions, up to 30 cyclic shifts may be configured. If 50 resourceelements in a symbol are used for the SRS transmission, up to 50 cyclicshifts may be configured. In one aspect, the number of cyclic shifts fora sequence may depend on a duration of the symbol and the delay spreadof the uplink channel.

In one aspect, if the UE 602 supports greater than comb-24 CSI-RSreceptions over a span of less than two resource blocks in a slot, theTRP 604 or the base station connected to the TRP 604 may generateconfiguration information for the UE 602 to receive CSI-RS on one ofevery 25 resource elements over a span of 1 resource blocks in a slot(e.g., use only 1 resource element in 1 resource block in a slot) toestimate the downlink channel for cluster management and scheduling. Inone example, the TRP 604 or the base station connected to the TRP 604may generate configuration information for the UE 602 to receive CSI-RSon one of every 24 resource elements as supported by the existing 5Gstandard but over a span of less than 24 resource blocks. In one aspect,the generated configuration information may include one of more of aperiodicity of the resource blocks, slots, subframes, etc., used for theCSI-RS receptions, a time hopping sequence used to transmit the CSI-RSby the TRP 604, the position of the first resource block used for theCSI-RS receptions, the position of the first resource element within theresource blocks used for the CSI-RS receptions, etc., in addition to thedensity of the resource elements and the number of resource blocksspanned by the resource elements used for the CSI-RS receptions.

In 612, the TRP 604 may transmit to the UE 602 the generatedconfiguration information for one or more SRS transmissions from the UE602 to the TRP 604 or configuration information for one or morereceptions by the UE 602 of CSI-RS transmitted from the TRP 604. In oneaspect, the TRP 604 may transmit the generated configuration informationin one or more of a radio resource control (RRC) message, a mediumaccess control (MAC) control element (CE), a non-access stratum (NAS)message, or downlink control information (DCI).

In 614, based on the configuration information received from the TRP604, the UE 602 may generate one or more SRS transmissions to the TRP604. Similarly, the UE may use the configuration information to receivethe CSI-RS transmitted from the TRP 604. In one aspect, if theconfiguration information indicates the UE 602 may transmit the SRS onevery resource element over a span of 1 resource block, the UE 602 maygenerate a first set of SRS on every resource element of a resourceblock in a slot. In one aspect, the UE 602 may generate a first set ofSRS on every resource element over a span of 2 resource blocks in aslot. The UE 602 may generate the first set of comb-1 SRS transmissionsor other dense SRS transmissions over a span of one or more resourceblocks in a slot for the TRP 604 or the base station connected to theTRP 604 to estimate the downlink channel for downlink transmissionprecoding.

In one aspect, if the configuration information indicates the UE 602 maytransmit the SRS on comb-5 SRS transmission or other comb-N SRStransmissions greater than comb-4, the UE 602 may generate a second setof SRS on one of every 5 resource elements or one of every resourceelements of values greater than 4 over a span of one or more resourceblocks in a slot for the TRP 604 or the base station connected to theTRP 604 to estimate the downlink channel for cluster management andscheduling. In one aspect, the UE 602 may generate a sequence and acyclic shift of the sequence used to transmit the second set of SRSbased on the configuration information. In one aspect, the UE 602 maygenerate a time hopping sequence and may generate the second set of SRSusing the time hopping sequence based on the configuration information.The density of the resource elements used for the first set of SRS maybe higher than the density of the resource elements used for the secondset of SRS. In other words, the comb value of the second set of SRS maybe greater than the comb value of the first set of SRS.

In one aspect, if the configuration information indicates the UE 602 mayreceive CSI-RS on one of every N resource elements over a span of one ormore resource blocks where N is 25 or other values greater than 24, theUE 602 may configure itself to receive the CSI-RS on one of every 25resource elements or one of every resource elements of values greaterthan 24 over a span of one or more resource blocks in a slot.

In 616, the UE 602 may transmit the generated first set of SRS to theTRP 604. For example, the UE 602 may transmit a first set of comb-1 SRStransmission over a span of one or more resource blocks in a slot forthe TRP 604 or the base station connected to the TRP 604 to estimate thedownlink channel for downlink transmission precoding. FIG. 7 illustratesan example of an SRS transmission over each resource element of aresource block that may span one resource block or two resource blocks.

In 618, the UE 602 may transmit the generated second set of SRS to theTRP 604. The second set of SRS may have a different density that thefirst set of SRS, and may be for different use by the TRP or basestation. For example, the UE 602 may transmit a second set of comb-5 SRStransmission over a span of one or more resource blocks in a slot forthe TRP 604 or the base station connected to the TRP 604 to estimate thedownlink channel for cluster management and scheduling. FIG. 8illustrates an example of an SRS transmission having an example density.

In 620, the UE 602 may receive a set of CSI-RS from the TRP 604 based onthe configuration information received in 612. For example, the UE 602may receive a set of CSI-RS on one of every 25 resource elements over aspan of one or more resource blocks in a slot. The UE 602 may measurethe CSI-RS resources and may transmit the measured CSI-RS resources tothe TRP 604 for the TRP 604 to estimate the downlink channel for clustermanagement and scheduling. FIG. 8 illustrates an example of an CSI-RStransmission having an example density.

FIG. 7 illustrates a configuration 700 of using every resource elementor subcarrier over a span of two resource blocks in a slot to transmitSRS resources from a UE to support precoding for downlink transmissionsin accordance with certain aspects of the disclosure. In the comb-1 SRStransmissions of FIG. 7, all twelve resource elements in the last symbolof each of the two resource blocks are used to transmit the SRS.

FIG. 8 illustrates a configuration 800 of using one of every 36 resourceelements or subcarriers over a number of resource blocks in a slot totransmit SRS resources from a UE to support cluster management andscheduling in accordance with certain aspects of the disclosure. In thecomb-36 transmissions of FIG. 8, the two resource elements used totransmit the SRS are separated by 36 resource elements in the lastsymbol over a span of four resource blocks in the slot. FIG. 8 may alsoillustrate a configuration of using one of every 36 resource elements orsubcarriers over a number of resource blocks in a slot to receive CSI-RSresources from a TRP to support cluster management and scheduling.

FIG. 9 is a flowchart 900 of a method of wireless communication that maybe implemented by a UE or a component of a UE (e.g., UE 104, 350, 504,602; the apparatus 1000, 1000′; the processing system 1114, which mayinclude the memory 360 and which may be the entire UE 350 or a componentof the UE, such as the TX processor 368, the RX processor 356, and/orthe controller/processor 359). The method may be performed by the UEconfigured to support CoMP. Optional aspects are illustrated with adashed line. The method may help the UE to transmit SRS and/or receiveCSI-RS in a more efficient manner that supports the unique needs ofcluster management and scheduling in CoMP and/or precoding for downlinktransmissions in CoMP.

At 902, the UE may transmit its supported configuration for uplink SRStransmission and/or its supported configuration for downlink CSI-RSreception for communication with a plurality of TRPs. The UE maytransmit the supported configuration information to one or more TRPs.For example, support component 1004 and/or transmission component 1002of apparatus 1000 may transmit the supported configuration. As use of ahigher density of the resource elements in a slot to transmit the SRSmay lead to more accurate estimates of the downlink channel and thusmore accurate precoding of the downlink transmissions from the TRPs tothe UE, the UE may support transmitting the SRS on every resourceelement (e.g., comb-1 SRS transmission). In one aspect, the UE maysupport transmitting the SRS over a span of an integer number ofresource blocks in a slot with a granularity of one resource block. Inone aspect, the UE may support transmitting the SRS on every resourceelement over a span of less than 4 resource blocks (e.g., 1, 2, or 3resource blocks) in a slot. In one aspect, to reduce the density of SRStransmission for cluster management and scheduling, the UE may supporttransmitting the SRS on one of every N resource elements over a span ofa number of resource blocks in a slot, where N is greater than 4.

In one aspect, to reduce the density of CSI-RS transmission by the TRPs,the UE may support receiving the CSI-RS on one of every N resourceelements over a span of a number of resource blocks in a slot, where Nis greater than 24. In one aspect, the UE may support receiving theCSI-RS over a span of less than 2 resource blocks in a slot. In oneaspect, the UE may support receiving more than a threshold number ofCSI-RS resources from a number of TRPs connected with the base stationduring a slot. In one aspect, the threshold number of CSI-RS resourcesreceived in a slot includes a threshold number of non-zero power (NZP)CSI-RS resources received in a component carrier during a slot, wherethe threshold number of NZP CSI-RS resources is greater than 32.

At 904, the UE may receive, in response to transmitting the supportedconfiguration(s), configuration information for SRS transmission(s) fromthe UE to the TRPs and/or configuration information for reception by theUE of CSI-RS(s) from the TRPs based on the supported configuration ofthe UE. For example, configuration component 1008 and/or receptioncomponent 1006 of apparatus 1000 may receive the configurationinformation. The configuration information may be received from the TRPsin one or more of an RRC message, a MAC CE, a NAS message, or a DCI. Thesupported configuration of the UE may set the upper bounds of theconfiguration information generated for the UE. In one aspect, if the UEsupports comb-1 SRS transmissions over a span of less than 4 resourceblocks in a slot, the UE may receive configuration information totransmit the SRS on every resource element over a span of 1 resourceblock in a slot. In another example, if the UE supports greater thancomb-4 SRS transmissions over a number of resource blocks in a slot, theUE may receive configuration information to transmit the SRS on one ofevery 5 resource elements over a span of two resource blocks in a slot.In one aspect, if the UE supports greater than comb-24 CSI-RS receptionsover a span of less than two resource blocks in a slot, the UE mayreceive configuration information for the UE to receive CSI-RS on one ofevery 25 resource elements over a span of 1 resource blocks in a slotfrom the TRPs.

At 906, the UE may communicate with at least a subset of the pluralityof TRPs using the SRS transmission(s) and/or the CSI-RS reception onresource elements assigned based on the configuration information. Basedon the configuration information received from the TRPs, the UE maygenerate one or more SRS transmissions to the TRPs or may configureitself to receive the CSI-RS transmitted from the TRPs. For example, thesupported configuration may comprise an SRS comb density supported bythe UE, and the UE's communication with at least a subset of the TRPsmay include transmitting the SRS transmission on resource elementsassigned based on the comb density supported by the UE. The SRStransmission may comprise a cyclic shift based on a number of theresource elements assigned for the SRS transmission. A number of cyclicshifts in a set of cyclic shifts for a sequence for the SRStransmissions may be based on a value of the comb density or a number ofresource elements assigned for the SRS transmission. In one aspect, ifthe configuration information indicates that the UE may transmit the SRSon every resource element over a span of 1 resource block, the UE maygenerate a first set of SRS on every resource element of a resourceblock in a slot. In one aspect, if the configuration informationindicates that the UE may transmit the SRS on comb-5 SRS transmission orother comb-N SRS transmissions greater than comb-4, the UE may generatea second set of SRS on one of every 5 resource elements or one of everyresource elements of values greater than 4 over a span of one or moreresource blocks in a slot. In one aspect, if the configurationinformation indicates that the UE may receive CSI-RS on one of every Nresource elements over a span of one or more resource blocks where N is25 or other values greater than 24, the UE may configure itself toreceive the CSI-RS on one of every 25 resource elements or one of everyresource elements of values greater than 24 over a span of one or moreresource blocks in a slot.

At 910, the UE may transmit a first set of SRS on one of every Mresource elements over an integer number of resource blocks in a slot tothe TRPs. For example, first set of SRS transmission component 1010and/or transmission component 1002 may transmit the first set of SRS.For example, the UE may transmit a first set of comb-1 SRS transmissionover a span of one or more resource blocks in a slot for the TRPs toestimate the downlink channel for downlink transmission precoding.

At 912, the UE may transmit a second set of SRS on one of every Jresource elements over a number of resource blocks in a slot to theTRPs. For example, second set of SRS transmission component 1012 and/ortransmission component 1002 may transmit the second set of SRS. J may belarger than M of 910 so that the density of SRS resources for the secondset of SRS may be less than the density of SRS resources for the firstset of SRS. For example, the UE may transmit a second set of comb-5 SRStransmission over a span of one or more resource blocks in a slot forthe TRPs to estimate the downlink channel for cluster management andscheduling.

At 914, the UE may receive a set of CSI-RS on one of every N resourceelements over a number of resource blocks in a slot from the TRPs, whereN is greater than 24. For example, CSI-RS component 1014 and/orreception component 1006 may receive the CSI-RS based on theconfiguration information received from the base station. For example,the UE may receive a set of CSI-RS on one of every 25 resource elementsover a span of one or more resource blocks in a slot from the TRPs. TheUE may measure the CSI-RS resources and may transmit the measured CSI-RSresources to the TRPs for the TRPs to estimate the downlink channel forcluster management and scheduling. In another example, the UE mayreceive the CSI-RS over a span of K resource blocks during a slot,wherein K is less than 2. The UE may receive the CSI-RS on one of everyM resource elements over a span of J resource blocks during a slot,wherein M is greater than or equal to N. Communicating with the subsetof the plurality of TRPs may comprise receiving, from one of theplurality of TRPs, the CSI-RS on one of every said M resource elementsover the span of J resource blocks during a first slot.

FIG. 10 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus1000 of a UE in accordance with certain aspects of the disclosure. Theapparatus 1000 may be the UE of 104, 350, 504, 602, or the apparatus1000′ to support CoMP. The apparatus 1000 may include a transmissioncomponent 1002, a support component 1004, a reception component 1006, aconfiguration component 1008, a first set of SRS transmission component1010, a second set of SRS transmission component 1012, and a CSI-RScomponent 1014.

The support component 1004 may be configured to generate the apparatus'ssupported configuration for uplink SRS transmission and its supportedconfiguration for downlink CSI-RS reception to one or more TRPs. Thesupported configuration may include transmitting the SRS on everyresource element (e.g., comb-1 SRS transmission), transmitting the SRSover a span of an integer number of resource blocks in a slot with agranularity of one resource block, transmitting the SRS on everyresource element over a span of less than 4 resource blocks (e.g., 1, 2,or 3 resource blocks) in a slot, transmitting the SRS on one of every Nresource elements over a span of a number of resource blocks in a slot,where N is greater than 4, etc. The supported configuration may includereceiving the CSI-RS on one of every N resource elements over a span ofa number of resource blocks in a slot, where N is greater than 24,receiving the CSI-RS over a span of K resource blocks in a slot, where Kis less than 2, etc.

The transmission component 1002 may be configured to transmit thesupported configuration of the SRS and CSI-RS generated by the supportedconfiguration of SRS and CSI-RS component 1014 to the base station 1050.The base station 1050 may correspond to, e.g., the base station 102,180, 310, 604, 1300, or the apparatus 1300′.

The configuration component 1008 may be configured to receive theconfiguration information for one or more SRS transmissions from theapparatus 1000 to the base station 1050 or configuration information forone or more receptions by the apparatus 1000 of CSI-RS transmitted fromthe base station 1050 based on the supported configuration of the UE.The configuration information may be received through the receptioncomponent 1006. The supported configuration of the UE may set the upperbounds of the configuration information generated for the UE. Theconfiguration information may indicate to the apparatus 1000 to transmitthe SRS on every resource element over a span of 1 resource block in aslot. In another aspect, the configuration information may indicate tothe apparatus 1000 to transmit the SRS on one of every 5 resourceelements over a span of two resource blocks in a slot. In one aspect,the configuration information may indicate to the apparatus 1000 toreceive CSI-RS on one of every 25 resource elements over a span of 1resource blocks in a slot from the base station 1050.

The configuration information may be used by the first set of SRStransmission component 1010 to generate a first set of SRS transmission.In one aspect, first set of SRS transmission component 1010 may beconfigured to generate a first set of SRS on every resource element of aresource block in a slot.

The configuration information may be used by the second set of SRStransmission component 1012 to generate the second set of SRStransmission. In one aspect, the second set of SRS transmissioncomponent 1012 may be configured to generate a second set of SRS one ofevery 5 resource elements or one of every resource elements of valuesgreater than 4 over a span of one or more resource blocks in a slot. Thefirst set of SRS transmission and the second set of SRS transmission maybe sent to the transmission component for transmission to the basestation 1050.

The configuration information may be used by the CSI-RS component 1014to receive the set of CSI-RS resources received from the base station1050 through the reception component 1006. The CSI-RS component 1014 maybe configured to receive the CSI-RS on one of every 25 resource elementsor one of every resource elements of values greater than 24 over a spanof one or more resource blocks in a slot.

FIG. 11 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1000′ of a UE employing a processingsystem 1114 in accordance with certain aspects of the disclosure. Theprocessing system 1114 may be implemented with a bus architecture,represented generally by the bus 1108. The bus 1108 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1114 and the overall designconstraints. The bus 1108 links together various circuits including oneor more processors and/or hardware components, represented by theprocessor 1104, the components 1010, 1012, 1014, 1016, 1018, and thecomputer-readable medium/memory 1106. The bus 1108 may also link variousother circuits such as timing sources, peripherals, voltage regulators,and power management circuits, which are well known in the art, andtherefore, will not be described any further.

The processing system 1114 may be coupled to a transceiver 1110. Thetransceiver 1110 is coupled to one or more antennas 1120. Thetransceiver 1110 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1110 receives asignal from the one or more antennas 1120, extracts information such asthe configuration information of the SRS and CSI-RS, or the CSI-RS fromthe received signal transmitted by the base station, and provides theextracted information to the processing system 1114, specifically thereception component 1006, the configuration information of SRS andconfiguration component 1008, and the CSI-RS component 1014. Inaddition, the transceiver 1110 receives information from the processingsystem 114, specifically the supported configuration of SRS and CSI-RS,the first set of SRS transmission, or the second set of SRStransmission, and based on the received information, generates a signalto be applied to the one or more antennas 1120. The processing system1114 includes a processor 1104 coupled to a computer-readablemedium/memory 1106. The processor 1104 is responsible for generalprocessing, including the execution of software stored on thecomputer-readable medium/memory 1106. The software, when executed by theprocessor 1104, causes the processing system 1114 to perform the variousfunctions described supra for any particular apparatus. Thecomputer-readable medium/memory 1106 may also be used for storing datathat is manipulated by the processor 1104 when executing software. Theprocessing system further includes at least one of the components 1002,1004, 1006, 1008, 1010, 1012, and 1014. The components may be softwarecomponents running in the processor 1104 configured to perform thestated processes/algorithm, resident/stored in the computer readablemedium/memory 1106 for implementation by the processor 1104, one or morehardware components specifically configured to carry out the statedprocesses/algorithm, one or more hardware components coupled to theprocessor 1104, or some combination thereof. Alternatively, theprocessing system 1114 may be the entire UE (e.g., see 350 of FIG. 3).

In one configuration, the apparatus 1000′ may include means forgenerating the supported configuration of SRS and CSI-RS by theapparatus 1000′. The means for generating the supported configuration ofSRS and CSI-RS may be implemented by the supported configuration of SRSand CSI-RS component 1014. The apparatus 1000′ may include means forreceiving the configuration information of SRS and CSI-RS from a basestation. The means for receiving the configuration information of SRSand CSI-RS from a base station may be implemented by the configurationinformation of SRS and CSI-RS component 1014. The apparatus 1000′ mayinclude means for generating the first set of SRS and means forgenerating the second set of SRS based on the configuration informationfor the SRS. The means for generating the first set of SRS may beimplemented by the first set of SRS transmission component 1010. Themeans for generating the second set of SRS may be implemented by thesecond set of SRS transmission component 1012. The apparatus 1000′ mayinclude means for receiving CSI-RS from the base station based on theconfiguration information for the CSI-RS. The means for receiving theCSI-RS from the base station may be implemented by the CSI-RS component1014.

FIG. 12 is a flowchart 1200 of a method of wireless communication thatmay be implemented by a base station in accordance with certain aspectsof the disclosure. The method may be performed by the TRP or basestation or a component of a base station (e.g., base station 102, 180,310, 604, apparatus 1300, 1300′ the processing system 1414, which mayinclude the memory 376 and which may be the entire base station 310 or acomponent of the base station 310, such as the TX processor 316, the RXprocessor 370, and/or the controller/processor 375). Optional aspectsare illustrated with a dashed line. The method may help the basestation/TRP to receive SRS and/or transmit CSI-RS in a more efficientmanner that supports the unique needs of cluster management andscheduling in CoMP and/or precoding for downlink transmissions in CoMP.

At 1202, the base station may receive, e.g., via one or more TRPsconnected to the base station, a supported configuration for uplink SRStransmission and/or the supported configuration for downlink CSI-RSreception by a UE. The reception may be performed by support component1306 and/or reception component 1304 in apparatus 1300. In one aspect,the base station may receive an indication that UE supports transmittingthe SRS on every resource element (e.g., comb-1 SRS transmission). Inone aspect, the base station may receive an indication that the UEsupports transmitting the SRS over a span of an integer number ofresource blocks in a slot with a granularity of one resource block. Inone aspect, the base station may receive an indication that the UEsupports transmitting the SRS on every resource element over a span ofless than 4 resource blocks (e.g., 1, 2, or 3 resource blocks) in aslot. In one aspect, to reduce the density of SRS transmission forcluster management and scheduling, the base station may receive anindication that the UE supports transmitting the SRS on one of every Nresource elements over a span of a number of resource blocks in a slot,where N is greater than 4.

In one aspect, to reduce the density of CSI-RS transmission by the TRPs,the base station may receive an indication that the UE supportsreceiving the CSI-RS on one of every N resource elements over a span ofa number of resource blocks in a slot, where N is greater than 24. Inone aspect, the base station may receive an indication that the UEsupports receiving the CSI-RS over a span of less than 2 resource blocksin a slot. In one aspect, the base station may receive an indicationthat the UE supports receiving more than a threshold number of CSI-RSresources from a number of TRPs connected with the base station during aslot. In one aspect, the threshold number of CSI-RS resources receivedin a slot includes a threshold number of non-zero power (NZP) CSI-RSresources received in a component carrier during a slot, where thethreshold number of NZP CSI-RS resources is greater than 32.

At 1204, the base station may generate configuration information for oneor more SRS transmissions from the UE to the base station orconfiguration information for one or more receptions by the UE of CSI-RStransmitted from the base station based on the supported configurationof the UE. For example, configuration component 1308 of apparatus 1300may generate the configuration information. The supported configurationof the UE may set the upper bounds of the configuration informationgenerated for the UE. In one aspect, the configuration information mayindicate to the UE to transmit the SRS on every resource element over aspan of 1 resource block in a slot. In another example, theconfiguration information may indicate to the UE to transmit the SRS onone of every 5 resource elements over a span of two resource blocks in aslot. In one aspect, the configuration information may indicate to theUE to receive CSI-RS on one of every 25 resource elements over a span of1 resource blocks in a slot from the TRPs.

At 1206, the base station may transmit through the TRPs the generatedconfiguration information to the UE. For example, the transmissioncomponent 1310 may transmit the configuration information. The subset ofthe TRPs that receive the supported configuration for the SRStransmission and the supported configuration for the CSI-RS reception bythe UE may be different from the subset of the TRPs that transmit thegenerated configuration information to the UE.

At 1208, the base station may communicate with the UE by receiving theSRS or transmitting the CSI-RS on resource elements assigned based onthe configuration information through a subset of the TRPs. The subsetof TRPs receiving the SRS or transmitting the CSI-RS may be differentfrom the subset of the TRPs that receive the supported configuration forthe SRS transmission and the supported configuration for the CSI-RSreception from the UE, or the subset of the TRPs that transmit thegenerated configuration information to the UE.

The supported configuration may comprise an SRS comb density supportedby the UE, and communicating with at least the subset of the pluralityof TRPs may include receiving the SRS transmission on resource elementsassigned by the base station based on the comb density supported by theUE. The SRS may comprise a cyclic shift based on a number of theresource elements assigned for the SRS transmission, and a number ofcyclic shifts in a set of cyclic shifts for a sequence for the SRS maybe based on a value of the comb density for the SRS or a number ofresource elements assigned for the SRS.

Based on the configuration information, the base station may receive oneor more SRS transmissions from the UE or may transmit the CSI-RS to theUE. In one aspect, if the configuration information indicates that theUE may transmit the SRS on every resource element over a span of 1resource block, the base station may receive a first set of SRS on everyresource element of a resource block in a slot. In one aspect, if theconfiguration information indicates that the UE may transmit the SRS oncomb-5 SRS transmission or other comb-N SRS transmissions greater thancomb-4, the base station may receive a second set of SRS on one of every5 resource elements or one of every resource elements of values greaterthan 4 over a span of one or more resource blocks in a slot. In oneaspect, if the configuration information indicates that the UE mayreceive CSI-RS on one of every N resource elements over a span of one ormore resource blocks where N is 25 or other values greater than 24, thebase station may transmit the CSI-RS on one of every 25 resourceelements or one of every resource elements of values greater than 24over a span of one or more resource blocks in a slot.

At 1210, the base station may receive a first set of SRS on one of everyM resource elements over an integer number of resource blocks in a slot.For example, first SRS component 1312 of apparatus 1300 may receive thefirst set of SRS. For example, the base station may receive a first setof comb-1 SRS transmission over a span of one or more resource blocks ina slot for the base station to estimate the downlink channel fordownlink transmission precoding.

At 1212, the base station may receive a second set of SRS on one ofevery J resource elements over a number of resource blocks in a slot.For example, second SRS component 1314 of apparatus 1300 may receive thesecond set of SRS. J may be larger than M of 910 so that the density ofSRS resources for the second set of SRS may be less than the density ofSRS resources for the first set of SRS. For example, the base stationmay receive a second set of comb-5 SRS transmission over a span of oneor more resource blocks in a slot for the base station to estimate thedownlink channel for cluster management and scheduling.

At 1214, the base station may transmit a set of CSI-RS on one of every Nresource elements over a number of resource blocks in a slot, where N isgreater than 24. For example, first CSI-RS component 1316 of apparatus1300 may transmit the CSI-RS. For example, the base station may transmita set of CSI-RS on one of every 25 resource elements over a span of oneor more resource blocks in a slot. The UE may measure the CSI-RSresources and may transmit the measured CSI-RS resources to the basestation for the base station to estimate the downlink channel forcluster management and scheduling.

FIG. 13 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an exemplary apparatus1300 that may comprise a base station or a component of a base stationin accordance with certain aspects of the disclosure. The apparatus 1300may be the base station of 102, 180, 310, 604, 1050. The apparatus 1300may include a reception component 1304, a support component 1306, aconfiguration component 1308, a transmission component 1310, a first SRScomponent 1312, a second SRS component 1314, a CSI-RS component 1316,and a downlink channel and link quality estimation component 1318.

The support component 1306 may be configured to receive the apparatus'ssupported configuration for uplink SRS transmission and its supportedconfiguration for downlink CSI-RS reception through the receptioncomponent 1304 from the UE 1350. The supported configuration may includetransmitting the SRS on every resource element (e.g., comb-1 SRStransmission), transmitting the SRS over a span of an integer number ofresource blocks in a slot with a granularity of one resource block,transmitting the SRS on every resource element over a span of less than4 resource blocks (e.g., 1, 2, or 3 resource blocks) in a slot,transmitting the SRS on one of every N resource elements over a span ofa number of resource blocks in a slot, where N is greater than 4, etc.

The configuration component 1308 may be configured to generate theconfiguration information for one or more SRS transmissions from UE tothe apparatus 1300 or configuration information for one or moretransmissions of CSI-RS from the base station to the UE 1350 based onthe supported configuration of the UE 1350. The configurationinformation may be transmitted through the transmission component 1310.The supported configuration of the UE may set the upper bounds of theconfiguration information generated for the UE. The configurationinformation may indicate to the UE 1350 to transmit the SRS on everyresource element over a span of 1 resource block in a slot. In anotheraspect, the configuration information may indicate to the UE 1350 totransmit the SRS on one of every 5 resource elements over a span of tworesource blocks in a slot. In one aspect, the configuration informationmay indicate to the UE 1350 to receive CSI-RS on one of every 25resource elements over a span of 1 resource blocks in a slot from thebase station 1050.

The configuration information may be used by the first SRS component1312 to receive a first set of SRS transmission from the UE 1350. In oneaspect, first SRS component 1312 may be configured to receive a firstset of SRS on every resource element of a resource block in a slot.

The configuration information may be used by the second SRS component1314 to receive the second set of SRS transmission from the UE 1350. Inone aspect, the second SRS component 1314 may be configured to receive asecond set of SRS one of every 5 resource elements or one of everyresource elements of values greater than 4 over a span of one or moreresource blocks in a slot. The first set of SRS transmission and thesecond set of SRS transmission may be received from the receptioncomponent 1304.

The configuration information may be used by the CSI-RS component 1316to transmit the set of CSI-RS resources to the UE 1350 through thetransmission component 1310. The CSI-RS component 1316 may be configuredto transmit the CSI-RS on one of every 25 resource elements or one ofevery resource elements of values greater than 24 over a span of one ormore resource blocks in a slot.

The downlink channel and link quality estimation component 1318 may beconfigured to estimate one or more downlink channels with the UE 1350based on the first set of SRS to determine precoding for downlinktransmission. The downlink channel and link quality estimation component1318 may also be configured to estimate a link quality of one or moreuplink channels or one or more downlink channels with the UE 1350 basedon one or more of the first set of SRS, the second set of SRS, ormeasurements of the CSI-RS by the UE 1350 transmitted from the UE 1350to the base station, e.g., apparatus 1300.

FIG. 14 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1300′ of a base station employing aprocessing system 1414 in accordance with certain aspects of thedisclosure. The processing system 1414 may be implemented with a busarchitecture, represented generally by the bus 1408. The bus 1408 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1414 and the overalldesign constraints. The bus 1408 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1404, the components 1410, 1412, 1414, 1416, 1418, andthe computer-readable medium/memory 1406. The bus 1408 may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, and power management circuits, which are well known in theart, and therefore, will not be described any further.

The processing system 1414 may be coupled to a transceiver 1410. Thetransceiver 1410 is coupled to one or more antennas 1420. Thetransceiver 1410 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1410 receives asignal from the one or more antennas 1120, extracts information such asthe supported configuration information of the SRS and CSI-RS, or theSRS from the received signal transmitted by the UE and provides theextracted information to the processing system 1114, specifically thereception component 1304, the supported configuration of SRS and CSI-RSby support component 1306, the first set of SRS component 1312, and thesecond SRS component 1314. In addition, the transceiver 1110 receivesinformation from the processing system 114, specifically theconfiguration information of SRS and CSI-RS, the CSI-RS transmission,and based on the received information, generates a signal to be appliedto the one or more antennas 1420. The processing system 1414 includes aprocessor 1404 coupled to a computer-readable medium/memory 1406. Theprocessor 1404 is responsible for general processing, including theexecution of software stored on the computer-readable medium/memory1406. The software, when executed by the processor 1404, causes theprocessing system 1414 to perform the various functions described suprafor any particular apparatus. The computer-readable medium/memory 1406may also be used for storing data that is manipulated by the processor1404 when executing software. The processing system further includes atleast one of the components 1404, 1406, 1408, 1410, 1412, 1414, 1416,and 1418. The components may be software components running in theprocessor 1104 configured to perform the stated processes/algorithm,resident/stored in the computer readable medium/memory 1406 forimplementation by the processor 1404, one or more hardware componentsspecifically configured to carry out the stated processes/algorithm, oneor more hardware components coupled to the processor 1404, or somecombination thereof. Alternatively, the processing system 1414 may bethe entire base station (e.g., see 310 of FIG. 3).

In one configuration, the apparatus 1300′ may include means forreceiving the supported configuration of SRS and CSI-RS by the UE. Themeans for receiving the supported configuration of SRS and CSI-RS by theUE may be implemented by the configuration information of SRS and CSI-RSby support component 1306. The apparatus 1300′ may include means forgenerating the configuration information of SRS and CSI-RS. The meansfor generating the configuration information of SRS and CSI-RS may beimplemented by the configuration information of SRS and CSI-RS forconfiguration component 1308. The apparatus 1300′ may include means forreceiving the first set of SRS and means for receiving the second set ofSRS based on the configuration information for the SRS. The means forreceiving the first set of SRS may be implemented by the first SRScomponent 1312. The means for receiving the second set of SRS may beimplemented by the second SRS component 1314. The apparatus 1300′ mayinclude means for transmitting CSI-RS based on the configurationinformation for the CSI-RS. The means for transmitting the CSI-RS fromthe base station may be implemented by the CSI-RS component 1314. Theapparatus 1300′ may include means for estimating one or more downlinkchannels using the first set of SRS or means for estimating a linkquality of one or more uplink channels or one or more downlink channelsbased on one or more of the first set of SRS, the second set of SRS, ormeasurements of the CSI-RS received by the apparatus 1300′. The meansfor estimating the downlink channels or means for estimating a linkquality of the uplink or downlink channels may be implemented by thedownlink channel and link quality estimation component 1318.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication by a userequipment (UE), comprising: transmitting a supported configuration ofthe UE for at least one of sounding reference signal (SRS) transmissionor channel state information reference signal (CSI-RS) reception forcommunication with a plurality of transmission reception points (TRPs);receiving, in response to transmitting the supported configuration,configuration information for at least one of the SRS transmission orthe CSI-RS reception, wherein the configuration information is generatedbased on the supported configuration; and communicating, with at least asubset of the plurality of TRPs, using at least one of the SRStransmission or the CSI-RS reception on resource elements assigned basedon the configuration information.
 2. The method of claim 1, wherein thesupported configuration comprises an SRS comb density supported by theUE, and wherein communicating with at least the subset of the pluralityof TRPs includes transmitting the SRS transmission on the resourceelements, which are assigned based on the SRS comb density supported bythe UE.
 3. The method of claim 2, wherein the SRS transmission is basedon a cyclic shift that is based on a number of the resource elementsassigned for the SRS transmission.
 4. The method of claim 1, wherein anumber of cyclic shifts in a set of cyclic shifts for a sequence for theSRS transmission is based on a value of a comb density for the SRStransmission or a number of the resource elements assigned for the SRStransmission.
 5. The method of claim 1, wherein the configurationinformation is received from the plurality of TRPs in one or more of aradio resource control (RRC) message, a medium access control (MAC)control element (CE), a non-access stratum (NAS) message, or a downlinkcontrol information (DCI).
 6. The method of claim 1, wherein thesupported configuration by the UE of the SRS transmission comprisesinformation indicating the UE supports one or more of transmitting theSRS transmission over a first span of an integer number of resourceblocks during a slot, transmitting the SRS transmission using everyresource element over a second span of one or more resource blocksduring the slot, or transmitting the SRS transmission using one of everyN resource elements over a third span of one or more resource blocksduring the slot, wherein N is greater than
 4. 7. The method of claim 6,wherein the configuration information received by the UE comprisesinformation configuring the UE to transmit a first set of SRS on eachresource element over the first span of a first integer number ofresource blocks during the slot.
 8. The method of claim 7, whereincommunicating with at least the subset of the plurality of TRPscomprises transmitting the first set of SRS on each resource elementover the first span of the first integer number of resource blocksduring a first slot.
 9. The method of claim 8, wherein the configurationinformation configures the UE to transmit a second set of the SRS on oneof every J resource elements over a fourth span of a second integernumber of resource blocks during the slot using a cyclic shift for asequence associated with the second set of the SRS, wherein J is greaterthan
 1. 10. The method of claim 9, wherein J is greater than four. 11.The method of claim 1, wherein the supported configuration of the UEcomprises a CSI-RS density supported by the UE and indicates that the UEsupports one or more of receiving the CSI-RS on one of every N resourceelements over a first span of one or more resource blocks during a slot,wherein N is greater than 24, or receiving the CSI-RS over a second spanof K resource blocks during the slot, wherein K is less than
 2. 12. Themethod of claim 11, wherein the configuration information configures theUE to receive the CSI-RS on one of every M resource elements over athird span of J resource blocks during the slot, wherein M is greaterthan or equal to N, and wherein communicating with at least the subsetof the plurality of TRPs comprises receiving, from one of the pluralityof TRPs, the CSI-RS on one of every said M resource elements over thethird span of J resource blocks during a first slot.
 13. The method ofclaim 1, wherein the supported configuration by the UE of the CSI-RSreception comprises information indicating the UE supports receivingmore than a threshold number of CSI-RS resources during a slot, whereinthe threshold number of CSI-RS resources during the slot comprises athreshold number of non-zero power (NZP) CSI-RS resources received in acomponent carrier during the slot, wherein the threshold number of NZPCSI-RS resources is greater than
 32. 14. A method of wirelesscommunication by a base station, comprising: receiving, from a userequipment (UE), a supported configuration of the UE for at least one ofsounding reference signals (SRS) transmission or channel stateinformation reference signals (CSI-RS) reception for communication witha plurality of transmission reception points (TRPs); generating, by thebase station, configuration information for at least one of the SRStransmission or the CSI-RS reception by the UE, wherein theconfiguration information is generated based on the supportedconfiguration received from the UE; transmitting the configurationinformation generated by the base station to the UE; and communicating,through at least a subset of the plurality of TRPs with the UE,including at least one of SRS reception from the UE or CSI-RStransmission to the UE on resource elements assigned based on theconfiguration information.
 15. The method of claim 14, wherein thesupported configuration comprises an SRS comb density supported by theUE, and wherein communicating with at least the subset of the pluralityof TRPs includes receiving the SRS transmission on the resource elementsassigned by the base station based on the SRS comb density supported bythe UE.
 16. The method of claim 14, wherein the SRS transmission isbased on a cyclic shift that is based on a number of the resourceelements assigned for the SRS transmission.
 17. The method of claim 14,wherein a number of cyclic shifts in a set of cyclic shifts for asequence for the SRS transmission is based on a value of a comb densityfor the SRS transmission or a number of the resource elements assignedfor the SRS transmission.
 18. The method of claim 14, wherein theconfiguration information generated by the base station is transmittedto the UE in one or more of a radio resource control (RRC) message, amedium access control (MAC) control element (CE), a non-access stratum(NAS) message, or a downlink control information (DCI).
 19. The methodof claim 14, wherein the supported configuration by the UE of the SRStransmission comprises information indicating the UE supports one ormore of transmitting the SRS transmission over a first span of aninteger number of resource blocks during a slot, transmitting the SRStransmission using every resource element over a second span of one ormore resource blocks during the slot, or transmitting the SRStransmission using one of every N resource elements over a third span ofone or more resource blocks during the slot, wherein N is greater than4.
 20. The method of claim 19, wherein the configuration informationgenerated by the base station comprises information configuring the UEto transmit a first set of SRS on one of every M resource elements overthe first span of the first integer number of resource blocks during theslot, wherein M is greater than or equal to
 1. 21. The method of claim20, wherein communicating with the UE comprises receiving from the UE,the first set of the SRS on one of every said M resource elements overthe first span of the first integer number of resource blocks during afirst slot, the method further comprising: estimating, by the basestation, one or more downlink channels with the UE based on the firstset of the SRS for determining precoding for one or more downlinktransmissions; and transmitting the one or more downlink transmissionsto the UE.
 22. The method of claim 20, wherein the configurationinformation comprises information configuring the UE to transmit asecond set of the SRS on one of every J resource elements over a fourthspan of a second integer number of resource blocks during the slot usinga cyclic shift for a sequence associated with the second set of the SRS,wherein J is greater than M, and wherein the cyclic shift is determinedin part based on a number of subcarriers in a symbol used to transmitthe second set of SRS, and wherein communicating with the UE comprisesreceiving, from the UE, the second set of the SRS on one of every said Jresource elements over the fourth span of the second integer number ofresource blocks during a second slot using the cyclic shift for thesequence.
 23. The method of claim 22, further comprising: obtaining bythe base station a link quality estimate of one or more uplink channelsor one or more downlink channels with the UE based on the first set ofthe SRS and the second set of the SRS for a coordinated multipointcommunication (CoMP) with the UE.
 24. The method of claim 14, whereinthe supported configuration by the UE of the CSI-RS reception comprisesinformation indicating the UE supports one or more of receiving theCSI-RS on one of every N resource elements over a first span of one ormore resource blocks during a slot, wherein N is greater than 24, orreceiving the CSI-RS over a second span of K resource blocks during theslot, wherein K is less than
 2. 25. The method of claim 24, wherein theconfiguration information generated by the base station comprisesinformation configuring the UE to receive the CSI-RS on one of every Mresource elements over a third span of J resource blocks during a slot,wherein M is greater than or equal to N, and wherein communicating withthe UE comprises transmitting the CSI-RS on one of every said M resourceelements over the third span of J resource blocks during a first slot.26. The method of claim 14, wherein the supported configuration by theUE of the CSI-RS reception comprises information indicating the UEsupports receiving more than a threshold number of CSI-RS resourcesduring a slot, and wherein the threshold number of CSI-RS resourcesduring the slot comprises a threshold number of non-zero power (NZP)CSI-RS resources received in a component carrier during the slot,wherein the threshold number of NZP CSI-RS resources is greater than 32.27. An apparatus for wireless communication at a user equipment (UE),comprising: a memory; an at least one processor coupled to the memoryand configured to: transmit a supported configuration of the UE for atleast one of sounding reference signal (SRS) transmission or channelstate information reference signal (CSI-RS) reception for communicationwith a plurality of transmission reception points (TRPs); receive, inresponse to transmitting the supported configuration, configurationinformation for at least one of the SRS transmission or the CSI-RSreception, wherein the configuration information is generated based onthe supported configuration; and communicate, with at least a subset ofthe plurality of TRPs, using at least one of the SRS transmission or theCSI-RS reception on resource elements assigned based on theconfiguration information.
 28. The apparatus of claim 27, wherein thesupported configuration comprises an SRS comb density supported by theUE, wherein communicating with at least the subset of the plurality ofTRPs includes transmitting the SRS transmission on the resource elementsassigned based on the SRS comb density supported by the UE, wherein theSRS transmission is based on a cyclic shift that is based on a number ofthe resource elements assigned for the SRS transmission, and wherein anumber of cyclic shifts in a set of cyclic shifts for a sequence for theSRS transmission is based on a value of the SRS comb density for the SRStransmission or a number of resource elements assigned for the SRStransmission.
 29. An apparatus for wireless communication at a basestation, comprising: a memory; and at least one processor coupled to thememory and configured to: receive, from a user equipment (UE), asupported configuration of the UE for at least one of sounding referencesignals (SRS) transmission or channel state information referencesignals (CSI-RS) reception for communication with a plurality oftransmission reception points (TRPs); generate, by the base station,configuration information for at least one of the SRS transmission orthe CSI-RS reception by the UE, wherein the configuration information isgenerated based on the supported configuration received from the UE;transmit the configuration information generated by the base station tothe UE; and communicate, through at least a subset of the plurality ofTRPs with the UE, including at least one of SRS reception from the UE orCSI-RS transmission to the UE on resource elements assigned based on theconfiguration information.
 30. The apparatus of claim 29, wherein thesupported configuration comprises an SRS comb density supported by theUE, and wherein communicating with at least the subset of the pluralityof TRPs includes receiving the SRS transmission on the resource elementsassigned by the base station based on the SRS comb density supported bythe UE, wherein the SRS transmission is based on a cyclic shift that isbased on a number of the resource elements assigned for the SRStransmission, and wherein a number of cyclic shifts in a set of cyclicshifts for a sequence for the SRS transmission is based on a value ofthe SRS comb density or a number of the resource elements assigned forthe SRS transmission.